hallucination

a sensory experience of something that does not exist outside the mind, caused by various physical and mental disorders, or by reaction to certain toxic substances, and usually manifested as visual or auditory images.

2.

the sensation caused by a hallucinatory condition or the object or scene visualized.

hallucination

n.

in the pathological/psychological sense of "seeing or hearing something which is not there," 1640s, from Latin hallucinationem (nominative hallucinatio), from past participle stem of hallucinari (see hallucinate). Hallucination is distinct from illusion in not necessarily involving a false belief. Related: Hallucinations.